1. Field of the Invention
The present invention relates to a magnetoresistive head that uses a spin-valve film as a magnetic sensor element for detecting magnetic signals while in contact with a magnetic recording medium.
2. Description of the Related Art
Magnetoresistive elements (hereinafter referred to as MR elements) utilize magnetoresistive effects where the resistance changes depending on the magnitude and direction of an external magnetic field, and are used in, for example, magnetic heads and the like as magnetic sensor elements for detecting the magnetic field of a signal from a magnetic recording medium.
A magnetic head equipped with such an MR element is generally called a magnetoresistive head (hereinafter referred to as MR head).
As such an MR element, one in which anisotropic magnetoresistive effects are utilized has been in use conventionally, but because its magnetoresistance ratio (MR ratio) is small, one in which a greater MR ratio is exhibited is desired, and in recent years, giant magnetoresistive elements (hereinafter referred to as GMR elements) using spin-valve films have been proposed (see, for example, non-patent document 1 or patent document 1).
A GMR element has a spin-valve film in which a non-magnetic layer is held by and between a pair of magnetic layers, and utilizes so-called giant magnetoresistive effects where the conductance of a sense current flowing in the plane direction with respect to the spin-valve film changes depending on the relative angle of magnetization of the pair of magnetic layers.
Specifically, the spin-valve film has a structure in which an anti-ferromagnetic layer, a pinned layer whose direction of magnetization is pinned in a predetermined direction by an exchange-coupling field at work between itself and the anti-ferromagnetic layer, a free layer whose magnetization direction changes depending on an external magnetic field, and a non-magnetic layer for magnetically isolating the pinned layer and the free layer are stacked.
In a GMR element using a spin-valve film, when an external magnetic field is applied, the magnetization direction of the free layer changes depending on the magnitude and direction of the external magnetic field. When the magnetization direction of the free layer is opposite (anti-parallel) the magnetization direction of the pinned layer, the resistance to the sense current flowing through the spin-valve film becomes greatest. On the other hand, when the magnetization direction of the free layer and the magnetization direction of the pinned layer are the same (parallel), the resistance to the sense current flowing through the spin-valve film becomes smallest.
Therefore, in a magnetic head equipped with such a GMR element (hereinafter referred to as a GMR head), when a given sense current is supplied to the GMR element, the voltage of the sense current flowing through the GMR element changes depending on the magnetic field of signals from a magnetic recording medium, and magnetic signals can be read from the magnetic recording medium by detecting the change in the voltage of the sense current.
In non-patent document 1, an example in which a GMR head is used in a hard disk drive is disclosed.
A hard disk drive has a structure in which, for example, a GMR head is mounted on a head slider attached to the tip of a suspension. The airflow that is generated by the rotation of the magnetic disk makes the head slider float above the signal recording surface of the magnetic disk, and reading operations with respect to the magnetic disk are performed by having magnetic signals that are recorded on the magnetic disk read by the GMR head mounted on the head slider.
Applications of the GMR head above are not limited to magnetic disk apparatuses, and in recent years, applications in magnetic tape apparatuses such as tape streamers and the like are being considered.
For example, a tape streamer that adopts a helical scan system has a structure in which a GMR head is positioned on the outer surface portion of a rotary drum such that it is oblique in accordance with the azimuth angle with respect to the direction that is substantially orthogonal to the running direction of the magnetic tape.
In the tape streamer, the magnetic tape runs obliquely with respect to the rotary drum, the rotary drum rotates, and reading operations for the magnetic tape are performed by reading the magnetic signals recorded on the magnetic tape while the GMR head mounted on the rotary drum and the magnetic tape slide in contact with each other.
In the tape streamer, because it is preferable that the distance between the GMR head and the magnetic tape, otherwise known as spacing, be kept small, in this respect, it is desirable that the surface of the magnetic tape be calendered.
However, as the surface of the magnetic tape becomes smoother, the contact area between the magnetic tape and the outer peripheral portion of the rotary drum increases, and the friction at work between the magnetic tape and the rotary drum while the tape is running becomes greater, thereby causing the magnetic tape and the rotary drum to stick, and it becomes difficult for the magnetic tape to run smoothly.
Therefore, the contact area with the outer peripheral portion of the rotary drum is made smaller, and the friction at work between the magnetic tape and the rotary drum smaller, by providing small protrusions on the surface of the magnetic tape using SiO2 fillers, organic fillers and the like.
In addition, a protective film, such as a DLC (diamond-like carbon) film or the like, for preventing damage or corrosion is formed on the surface of the magnetic tape.
In the hard disk drive described above, reading operations are performed under conditions in which the GMR head is not in contact with the signal recording surface of the magnetic disk. In addition, Cu is ordinarily used for the non-magnetic layer constituting part of the spin-valve film, and on the surface of the GMR head that faces the magnetic disk, a protective film, such as a DLC film or the like, for preventing Cu from becoming corroded is formed.
[Non-Patent Document 1]
“Giant Magnetoresistance in Soft Ferromagnetic Multilayers” Physical Review B, Volume 43, Number 1, pages 1297˜1300
[Patent Document 1]
Japanese Patent Application Publication Hei-8-111010